Introduction: Toxoplasma gondii is an intracellular protozoan that may disrupt the traditional cell barriers against cancer, allowing the accumulation of oncogenic mutations over time. Our research aimed to explore the relationship between T. gondii infection and tumor development. Methodology: The anti-T. gondii IgG and IgM antibodies were tested for156 patients with tumors (51 with breast cancer, 20 with hepatoma, 20 with larynx carcinoma, 20 with squamous cell carcinoma of bone, 16 with lymphoma, 13 with brain tumor, 4 with bladder cancer and 12 with benign uterine tumor) and 90 healthy controls by using electrochemiluminescence immunoassay. Tissue specimens were collected from T. gondii seropositive cases for histological and immunohistochemistry (IHC) examinations. Results: The seroprevalence of human toxoplasmosis in the Sharkia Governorate, Egypt is significantly correlated with various types of tumors: breast cancer in 49 subjects (96.1%), and squamous cell carcinoma of bone in 16 subjects (80%). It was also present in nine cases of brain tumors. Anti-Toxoplasma IgG was detected in seven cases of liver tumors and one-quarter of bladder cancer. The anti- Toxoplasma IgM was present in three patients with benign uterine tumors, one patient with a bone tumor and two patients with breast cancer. Toxoplasma cysts were detected in immunostained brain sections. Conclusion: The correlation between T. gondii infection and tumors was established by this study indicating a significant emerging role of human toxoplasmosis in the etiology or existence of particular types of tumors.